scholarly journals The effect of anisotropic flow properties on ice-sheet surface elevation change

2004 ◽  
Vol 39 ◽  
pp. 439-444 ◽  
Author(s):  
Weili Wang ◽  
Jun Li ◽  
Jay Zwally ◽  
Vin Morgan ◽  
Tas D. Van Ommen
Keyword(s):  
Strain Rate ◽  
Ice Sheet ◽  
Surface Elevation ◽  
Ice Thickness ◽  
Flow Properties ◽  
Elevation Change ◽  
Ice Flow ◽  
Anisotropic Flow ◽  
Sheet Surface ◽  
Surface Elevation Change

AbstractAn ice-flow model has been developed and applied to Law Dome, East Antarctica, at the location of the Dome Summit South deep borehole. The results are used to reconstruct an ice-sheet history of accumulation rate, ice thickness and the rate of change in ice thickness. The focus of this study is on the effect of the variation in anisotropic flow properties on the ice-sheet surface elevation change. The enhancement factor, defined as the ratio of the strain rate for anisotropic ice to the strain rate for isotropic ice, is used in the ice-flow relations to account for the anisotropic properties of the ice with fabric development. The model is run with the various ice rheologies which represent anisotropic or isotropic ice-flow properties. The results show that the model incorporating anisotropic flow properties of the ice is more sensitive to the climate-change history.

scholarly journals Modeling of firn compaction for estimating ice-sheet mass change from observed ice-sheet elevation change

2011 ◽  
Vol 52 (59) ◽  
pp. 1-7 ◽  
Author(s):  
Jun Li ◽  
H. Jay Zwally
Keyword(s):  
Accumulation Rate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temporal Variations ◽  
Mass Change ◽  
Surface Elevation ◽  
Effective Density ◽  
Elevation Change ◽  
Surface Elevation Change ◽  
Elevation Changes

AbstractChanges in ice-sheet surface elevation are caused by a combination of ice-dynamic imbalance, ablation, temporal variations in accumulation rate, firn compaction and underlying bedrock motion. Thus, deriving the rate of ice-sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion, which do not involve changes in mass, and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability. We use a 25 year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model. We apply this formulation to ICESat measurements of surface elevation change at three locations on the Greenland ice sheet in order to separate the accumulation-driven changes from the ice-dynamic/ablation-driven changes, and thus to derive the corresponding mass change. Our calculated densities for the accumulation-driven changes range from 410 to 610 kgm–3, which along with 900 kgm–3 for the dynamic/ablation-driven changes gives average densities ranging from 680 to 790 kgm–3. We show that using an average (or ‘effective’) density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign.

scholarly journals Four decades of surface elevation change of the Antarctic Ice Sheet from multi-mission satellite altimetry

2018 ◽  
Author(s):  
Ludwig Schröder ◽  
Martin Horwath ◽  
Reinhard Dietrich ◽  
Veit Helm
Keyword(s):  
Time Series ◽  
Satellite Altimetry ◽  
Ice Sheet ◽  
Surface Elevation ◽  
Elevation Change ◽  
Antarctic Ice Sheet ◽  
Mission Satellite ◽  
Surface Elevation Change ◽  
Precipitation Anomalies ◽  
The Antarctic

Abstract. We developed an approach for a multi-mission satellite altimetry analysis over the Antarctic Ice Sheet which comprises Seasat, Geosat, ERS-1, ERS-2, Envisat, ICESat and CryoSat-2. In a first step we apply a consistent reprocessing of the radar alitmetry data which improves the measurement precision by up to 50 %. We then perform a joint repeat altimetry analysis of all missions. We estimate inter-mission offsets by approaches adapted to the temporal overlap or non-overlap and to the similarity or dissimilarity of involved altimetry techniques. Hence, we obtain monthly grids forming a combined surface elevation change time series. Owing to the early missions Seasat and Geosat, the time series span almost four decades from 07/1978 to 12/2017 over 25 % of the ice sheet area (coastal regions of East Antarctica and the Antarctic Peninsula). Since the launch of ERS-1 79 % of the ice sheet area is covered by observations. Over this area, we obtain a negative volume trend of −34 ± 5 km3 yr−1 for the more than 25-year period (04/1992–12/2017). These volume losses have significantly accelerated to a rate of −170 ± 11 km3 yr−1 for 2010–2017. Interannual variations significantly impact decadal volume rates which highlights the importance of the long-term time series. Our time series show a high coincidence with modeled cumulated precipitation anomalies and with satellite gravimetry. This supports the interpretation with respect to snowfall anomalies or dynamic thinning. Moreover, the correlation with cumulated precipitation anomalies back to the Seasat and Geosat periods highlights that the inter-mission offsets were successfully corrected and that the early missions add valuable information.

scholarly journals Re-evaluation of paleo-accumulation parameterization over Northern Hemisphere ice sheets during the ice age examined with a high-resolution AGCM and a 3-D ice-sheet model

2005 ◽  
Vol 42 ◽  
pp. 433-440 ◽  
Author(s):  
Takateru Yamagishi ◽  
Ayako Abe-Ouchi ◽  
Fuyuki Saito ◽  
Tomonori Segawa ◽  
Teruyuki Nishimura
Keyword(s):  
High Resolution ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Ice Sheet ◽  
Precipitation Change ◽  
Ice Age ◽  
Surface Elevation ◽  
Laurentide Ice Sheet ◽  
Elevation Change ◽  
Surface Elevation Change

AbstractSimulations of the Northern Hemisphere ice sheet at the Last Glacial Maximum (LGM; 21 kyr BP) are performed using a high-resolution atmospheric general circulation model (AGCM) in order to re-evaluate the conventional surface temperature- or elevation-based parameterization. The influence of precipitation change on the steady-state topography of the Laurentide ice sheet at the LGM is estimated using an AGCM with a horizontal resolution of ∼1° and a three-dimensional thermomechanically coupled ice-sheet model. The ice volume estimated by the AGCM simulation is much larger than that indicated by the conventional parameterization. Through sensitivity analysis of the AGCM and ice-sheet model, it is found that the rate of precipitation change depends on the location of the ice sheet, and that the rate of precipitation change due to surface elevation change is higher than the rate unrelated to surface elevation change on the Laurentide ice sheet. The rate of precipitation is also shown to exhibit seasonality and regionality due to effects such as interior desertification and the concentration of storm tracks.

scholarly journals Rapid changes of Alpine glaciers in Austria tracked by ALS surveys 

2021 ◽  
Author(s):  
Kay Helfricht ◽  
Lea Hartl ◽  
Martin Stocker-Waldhuber ◽  
Bernd Seiser ◽  
Andrea Fischer
Keyword(s):  
Relative Volume ◽  
Surface Elevation ◽  
Ice Thickness ◽  
Mountain Range ◽  
Volume Loss ◽  
Elevation Change ◽  
Thickness Change ◽  
Alpine Glaciers ◽  
Glacier Changes ◽  
Surface Elevation Change

<p>Unprecedented glacier changes are reported for many mountain regions on earth based on surveys with different spatial resolution and repeat intervals. Eastern Alpine glaciers have been receding since the LIA maximum, with increasing relative volume loss at the beginning of the 21<sup>st</sup> century. New high-resolution data of surface elevation from ALS surveys enable the analysis of most recent glacier changes at three mountain ranges in western Austria as an impact of climate change.</p><p>Surface elevation change rates between 2007 and 2018 increased again in comparison to former periods. Volume loss takes place even in the highest elevation zones, and most of the glaciers are out of an equilibrium state, such that consolidation of mass balance towards zero appears impossible under present climate conditions. The disintegration of low lying glacier tongues and a strong depletion of the firn cover are further signs of rapid glacier changes. The frequency distributions of surface elevation change throughout the area of each glacier show distinct shifts in peak ice thickness change and patterns of surface change distribution that suggest ongoing processes of glacier disintegration. Combining recent surface elevation changes and estimations of the spatial distribution of ice thickness in Austria shows that most of glaciers will vanish in 50 years or less. Only glaciers currently larger than 5 km² can be expected to exist longer at reduced size. At current rates of mass loss, glaciers are projected to retreat entirely to above 2800m in the Ötztal and Stubai ranges by 2050. Further concerns arise regarding methods of tracking the future development of the remaining ice bodies. In particular, in the Silvretta mountain range, the majority of glacier margins have to be delineated in debris-covered glacier zones. It is debatable whether some of the smallest glaciogenic features should still be accounted for in glacier inventories or moved to an inventory of transient cryogenic landforms.</p>

scholarly journals ICE SHEET ELEVATION MAPPING AND CHANGE DETECTION WITH THE ICE, CLOUD AND LAND ELEVATION SATELLITE-2

2019 ◽  
Vol XLII-2/W13 ◽  
pp. 1747-1751 ◽  
Author(s):  
B. M. Csatho ◽  
A. F. Schenk ◽  
T. Neumann
Keyword(s):  
Time Series ◽  
Change Detection ◽  
Ice Sheet ◽  
Simulated Data ◽  
Surface Elevation ◽  
Elevation Change ◽  
Laser Altimetry ◽  
Calibration And Validation ◽  
Ice Cloud ◽  
Surface Elevation Change

<p><strong>Abstract.</strong> On September 15, 2018, ICESat-2 (Ice, Cloud, and land Elevation satellite) was successfully launched to measure ice sheet and glacier elevation change, sea ice freeboard, and vegetation. This paper describes the computation of surface elevation change rates obtained with SERAC (Surface Elevation Reconstruction And Change detection) from ICESat-2 observations. After summarizing some relevant aspects of ICESat-2 and its sole instrument ATLAS (Advanced Topographic Laser Altimetry System) the paper focuses on how we calculate time series of elevation change rates from ICESat-2’s data product ATL03. Since real ICESat-2 data suitable for generating time series of several time epochs are not yet available, we used simulated data for this study. We will start generating time series from real ICESat-2 data after the conclusion of the ongoing calibration and validation phase and we expect to present real-world examples at the WG III/9 meeting in June, 2019 in Enschede, The Netherlands.</p>

scholarly journals Derivation of ice thickness and bedrock topography in data-gap regions over Antarctica

2000 ◽  
Vol 31 ◽  
pp. 191-197 ◽  
Author(s):  
Roland C. Warner ◽  
W. F. Budd
Keyword(s):  
Ice Sheet ◽  
Ice Thickness ◽  
Ice Flow ◽  
Sheet Surface ◽  
Bedrock Topography ◽  
Ice Accumulation ◽  
Data Gap ◽  
Lambert Glacier ◽  
The Antarctic ◽  
Lambert Glacier Basin

AbstractAn approach to deriving the thickness of the Antarctic ice sheet and inferring the bedrock elevation to fill in gaps in the compilations of ice-thickness observations is presented. It combines assumptions about the general state of balance of the ice sheet and of the dynamics of ice flow, with information about ice accumulation and the topography of the ice-sheet surface elevation to infer the ice thickness and bedrock. A simplified version of the scheme already shows the potential of this approach, as is demonstrated by an application to the Lambert Glacier basin, East Antarctica.

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